S3C80A5B
CLOCK CIRCUITS
7-3
SYSTEM CLOCK CONTROL REGISTER (CLKCON)
The system clock control register, CLKCON, is located in set 1, address D4H. It is read/write addressable and has
the following functions:
— Oscillator frequency divide-by value
CLKCON register settings control whether or not an external interrupt can be used to trigger a Stop mode release.
(This is called the "IRQ wake-up" function.) The IRQ wake-up enable bit is CLKCON.7. In S3C80A5B, this bit is not
valid any more. Actually bit 7, 6, 5, 2, 1, and 0 are no meaning in S3C80A5B.
After a reset, the main oscillator is activated, and the f
OSC
/16 (the slowest clock speed) is selected as the CPU
clock. If necessary, you can then increase the CPU clock speed to f
OSC
, f
OSC
/2, or f
OSC
/8.
System Clock Control Register (CLKCON)
D4H, Set 1, R/W
.7
.6
.5
.4
.3
.2
.1
.0
MSB
LSB
Divide-by selection bits for
CPU clock frequency:
00 = f
OSC
/16
01 = f
OSC
/8
10 = f
OSC
/2
11 = f
OSC
(non-divided)
Not used
Not used
Not used
Figure 7-4. System Clock Control Register (CLKCON)